Methanol-to-olefin processes are well described in the art. Typically, methanol-to-olefin processes are used to produce predominantly ethylene and propylene. An example of such a methanol-to-olefin process is described in WO-A 2006/020083. In the process of WO-A 2006/020083 the methanol is first converted into dimethylether (DME) prior to be subjected to a conversion to olefins, thereby reducing the amount of water produced during the conversion to olefins. Both methanol and DME are suitable feedstocks for a methanol-to-olefin process and therefore such processes are also generally referred to as oxygenate-to-olefin (OTO) processes.
In the process of WO-A 2006/020083, the methanol or DME is contacted with a catalyst at temperatures above 200° C. At temperatures above 200° C., and in particular above 350° C., however, an undesired decomposition of the methanol and/or DME can take please before the methanol and/or DME can be converted to the desired olefinic product. This decomposition may for instance take place during the preheating of the oxygenate feed or during the introduction of the oxygenate feed into the reactor by contact with metal surfaces of for instance the reactor wall, internals or nozzles. The metal in the metal surfaces catalyses the decomposition of methanol into hydrogen and carbon monoxide.
In for instance EP1513787 it is suggested to maintain the inner surface of the feed nozzles at a temperature below 350° C., even as low as 150° C., to prevent undesired decomposition of oxygenates in the feedstock leading to the formation of waste by-products.
However, this requires extensive cooling and insulation of the feed nozzles, while the feed is introduced into the reactor at a lower than desired temperature.
There is a need in the art for an OTO process wherein undesired decomposition of the feed is reduced.